System and method for latency reduction for automatic speech recognition using partial multi-pass results

ABSTRACT

A system and method is provided for reducing latency for automatic speech recognition. In one embodiment, intermediate results produced by multiple search passes are used to update a display of transcribed text.

PRIORITY

The present application is a continuation of Ser. No. 10/742,852, filedDec. 23, 2003, the contents of which is incorporated herein by referencein its entirety.

BACKGROUND

1. Field of the Invention

The present invention relates generally to speech recognition systemsand, more particularly, to a system and method for latency reduction forautomatic speech recognition using partial multi-pass results.

2. Introduction

Automatic speech recognition (ASR) is a valuable tool that enablesspoken audio to be automatically converted into textual output. Theelimination of manual transcription represents a huge user benefit.Thus, whether applied to the generation of transcribed text, theinterpretation of voice commands, or any other time-saving application,ASR is presumed to have immense utility.

In practice, however, ASR comes at a great computational cost. Ascomputing technology has improved, so has the complexity of thecomputation models being applied to ASR. Computing capacity is rarelywasted in the ever continuing search for accuracy and speed in therecognition of speech.

These two criteria, accuracy and speed, in particular represent thethresholds by which user adoption and acceptance of the technology aregoverned. Quite simply, if the promise of the technology exceeds thepractical benefit in real-world usage, the ASR technology quickly movesinto the category of novelty, not usefulness.

Conventionally, high accuracy ASR of continuous spontaneous speechrequires computations taking far more time than the duration of thespeech. As a result, a long latency exists between the delivery of thespeech and the availability of the final text transcript. What is neededtherefore is a mechanism that accommodates real-world ASR latencieswithout sacrificing application usefulness.

SUMMARY

In accordance with the present invention, a process is provided forreducing latency for automatic speech recognition. In one embodiment,intermediate results produced by multiple search passes are used toupdate a display of transcribed text.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. Thefeatures and advantages of the invention may be realized and obtained bymeans of the instruments and combinations particularly pointed out inthe appended claims. These and other features of the present inventionwill become more fully apparent from the following description andappended claims, or may be learned by the practice of the invention asset forth herein.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited and otheradvantages and features of the invention can be obtained, a moreparticular description of the invention briefly described above will berendered by reference to specific embodiments thereof which areillustrated in the appended drawings. Understanding that these drawingsdepict only typical embodiments of the invention and are not thereforeto be considered to be limiting of its scope, the invention will bedescribed and explained with additional specificity and detail throughthe use of the accompanying drawings in which:

FIG. 1 illustrates an embodiment of a system of the present invention;

FIG. 2 illustrates an embodiment of a user interface for navigatingtranscription data; and

FIG. 3 illustrates a flowchart of a method of the present invention.

DETAILED DESCRIPTION

Various embodiments of the invention are discussed in detail below.While specific implementations are discussed, it should be understoodthat this is done for illustration purposes only. A person skilled inthe relevant art will recognize that other components and configurationsmay be used without parting from the spirit and scope of the invention.

Access to speech data is becoming increasingly prevalent due to theubiquitous nature of digitized storage. In particular, digitized storagehas enabled public, corporate, and private speech data to be easilytransferred over public and private networks. With increasing frequency,speech content is being recorded, archived and distributed on demand tointerested users.

While access to speech content is increasing, its usability has remainedrelatively stagnant. This results from the nature of speech as a serialmedium, an inherent characteristic that demands serial playback in itsretrieval. Even with conventional technologies that can increase therate of playback, the fundamental disadvantages in access to the speechcontent remain.

It is a feature of the present invention that access to speech contentis improved through the removal of inherent difficulties of speechaccess. As will be described in greater detail below, serial access tospeech content is replaced by an efficient graphical user interface thatsupports visual scanning, search and information extraction oftranscription text generated from the speech content.

As is well known in the art, automatic speech recognition (ASR)represents an evolving technology that enables the generation oftranscription data from speech content. ASR has shown increasingpotential as new generations of ASR technology have leveraged thecontinual advances in computing technology. Notwithstanding theseadvancements, ASR technology has not yet broken into a full range ofuses among every day tasks. This has likely resulted due to fundamentalissues of transcription accuracy and speed.

As would be appreciated, typical applications of ASR technology arefaced with a tradeoff between transcription accuracy and speed. Quitesimply, increased transcription accuracy often requires more complexmodeling (e.g., acoustic and language model), the inevitable consequenceof which is increased processing time. This increased processing timecomes at an ever-increasing penalty as it goes significantly beyond thereal time (or actual) rate of the speech content. The delay incompletion (or latency) of the speech processing can often become theprimary reason that bars a user from accepting the application of theASR technology in a given context.

User acceptance being a key, what is needed is a user interface thatenhances a user's experience with transcription data. Prior toillustrating the various features of the present invention, reference ismade first to the generic system diagram of FIG. 1. As illustrated,system 100 includes a processing system 110 that includes ASR module112. In one embodiment, processing system 110 is a generic computersystem. ASR module 112 is generally operative on spoken audio datastored in audio source 130. As would be appreciated, audio source 130may be representative of a storage unit that may be local or remote toprocessing system 110. In other scenarios, audio source 130 may berepresentative of a transmission medium that is providing live contentto processing system 110. Upon receipt of audio data from audio source130, ASR module 112 would be operative to generate text data that wouldbe displayable in user interface 130.

An embodiment of user interface 130 is illustrated in FIG. 2. Asillustrated, user interface 200 includes three primary element areas,including speech header section 210, text transcription section 220, andtext segment identifier section 230. In general, speech header section210 includes some form of identifying information for various speechcontent (e.g., public speeches, lectures, audio books, voice mails,etc.) that is accessible through user interface 200. In one embodiment,selection of a particular speech header in speech header section 210initiates replay of the speech content along with the generation oftranscription text that appears in transcription section 220. Asillustrated in FIG. 2, selection of Speech 2 Header produces a displayof its corresponding transcription text in transcription section 220.

In an example related to a voice mail embodiment, speech header section210 could be designed to include information such as the caller's name,the date of the voice mail, the length of the voice mail, etc; texttranscription section 220 could be designed to include the transcriptiontext generated from a selected voice mail; and speech header section 230could be designed to include keywords for segments of the selectedvoicemail.

As further illustrated in FIG. 2, transcription section 220 can bedesigned to display transcription text as text segments 1-N. In oneembodiment, text segments 1-N are formatted into audio paragraphs usingan acoustic segmentation algorithm. In this process, segments areidentified using pause duration data, along with information aboutchanges in acoustic signal energy. As would be appreciated, the specificformatting of the transcription text into text segments 1-N would beimplementation dependent in accordance with any criteria that would befunctionally useful for a viewing user.

In one embodiment, text segments can also have associated therewith anidentifier that relates to the text segment. These identifiers aredisplayed in text segment identifier section 230 and can be collectivelyused to enable a user to intelligently navigate through the transcribedtext. As would be appreciated, the specific form of the text segmentidentifiers would be implementation dependent in accordance with anycriteria that would be functionally useful for a viewing user. In oneexample, the text segment identifiers could represent one or morekeywords that were extracted from the corresponding transcription textsegment.

As noted, one of the goals of user interface 200 is to improve upon auser's experience in interacting with transcription text. A significantdrawback in this process is the relevant tradeoff between transcriptionaccuracy and speed. Indeed, conventional ASR technology that producesreasonably accurate text can be expected to run at a rate four timesthat of real time. This delay in the generation of transcription textrepresents a real impediment to a user's adoption of the technology. Itis therefore a feature of the present invention that user interface 200is designed to accommodate a user's sense of both transcription speedand accuracy. As will be described in greater detail below, this processleverages transcription efforts that incrementally improve upontranscription accuracy.

To obtain high accuracy transcripts for continuous spontaneous speech,several normalization and adaptation algorithms can be applied. Thesetechniques can take into account the specific channel conditions as wellas the gender, vocal tract length and dialect of the speaker. The modelparameters for the compensation/adaptation model can be estimated attest time in an unsupervised fashion. The unsupervised algorithms use aninitial guess at the transcription of the speech. Based on that guessand the audio, an adapted/normalized model is estimated and are-transcription with the adapted/normalized model improves the accuracyof the transcript. The final, most accurate transcript is obtained byiterative transcription with models adapted/normalized in multiplestages. Hence this process can be referred to as multi-passtranscription.

The ASR transcription passes are computationally expensive. To expresstheir cost, the processing time is related to the duration of the speechand the quotient of the two expresses the computation cost in terms of areal-time factor. In one embodiment, to reduce the computational cost ofrepeated transcription passes, the initial search pass produces aword-graph representing a few of the possible transcriptions deemed mostlikely by the current model. Subsequent transcription passes, using themore accurate adapted/normalized model, only consider the transcriptionsenumerated by the word-graph, dramatically reducing the computationalcost of transcription.

The first recognition pass, which uses an unadapted/unnormalized modeland performs an unconstrained search for the transcript, takes about 4times real-time time. On an independent test set, the word-accuracy ofthis transcript was 74.2%. Besides an initial guess of the transcript,this search pass produces a word-graph that is used in subsequent searchpasses.

The second recognition pass estimates the gender and vocal tract of thespeaker based on the audio and the transcript produced in the firstpass. A second search pass is then performed, constrained by theword-graph produced by the first pass. In one embodiment, this secondsearch pass uses a Gender Dependent (GD), Vocal Tract Length Normalized(VTLN) model (based on the unsupervised gender estimate) and uses VTLNacoustic features (based on the unsupervised vocal tract lengthestimate). The result of this search pass is a new transcript. Theword-accuracy of this second transcript was 77.0% (a 2.8% absoluteimprovement over the first pass accuracy). The computation cost of thissecond pass is about 1.5 times real-time.

The third recognition pass uses two adaptation algorithms to adapt tothe channel and speaker characteristics of the speaker. Again, this isperformed in an unsupervised way, using the audio and the transcript ofthe second (VTLN) pass. It estimates two linear transformations, oneapplied to the acoustic features using Constrained Model-spadeAdaptation (CMA) and one applied to the model mean parameters usingMaximum Likelihood Linear Regression (MLLR). First the CMA transform isestimated using the VTLN transcript and the audio. Then a search pass isperformed, again constrained by the word-graph from the first pass,using the CMA rotated acoustic features and the GD VTLN model. Thetranscript from that pass is then used with the audio to estimate theMLLR transform. After rotating the model means using that transform,another word-graph constrained search pass is executed that provides thethird pass transcript. The total processing time of this adaptation passis about 1.5 times real-time. The adaptation pass transcript is thefinal system output and improves the accuracy to 78.4% (a 1.4% absoluteimprovement over the VTLN pass result).

Since the first pass still represents a large latency of 4 timesreal-time, an initial search pass is performed before running the firstpass, referred to as the Quick Pass. This output from this pass is notused in the multi-pass recognition process but is simply used as a lowlatency result for presentation to the user. It can be obtained in aboutone times real time. Here, the exact rate of the initial pass as beingat real time or slightly greater than real time is not a criticalfactor. Rather, one of the goals of the initial pass is to produce aresult for the user as quickly as possible.

The run-time reduction of the initial pass as compared to the first passcan be obtained by reducing the search beam used internally in therecognizer. As a result, the speed-up comes at an accuracy cost: theQuick Pass accuracy was 68.7% (a 5.5% absolute degradation compared tothe first pass result).

It is a feature of the present invention that the intermediate guessesat the transcript of the speech can be presented to the user at lowerlatency than the final, most accurate transcript. In other words, theresults of each of the search passes enables the developer to produce amore usable interface by presenting the best quality results availableat the time of the user request.

Thus, in one embodiment, the particular search pass can be indicated inthe interface by using color shading or explicitly indicating whichtranscript the user is currently viewing. For example, as illustrated inFIG. 2, Text Segment N is displayed in a different shade or color,thereby indicating that further, more accurate transcription resultswould be forthcoming. In other embodiments, the user interface can bedesigned to show the user how many additional transcription passes areforthcoming, the estimated transcription accuracy rate, etc.

With this approach, when a one-minute speech file is being processed, arough transcript can be displayed in the interface within the firstminute, so that users can begin working with the intermediate results.As each pass is completed, the display is updated with the newinformation. After eight minutes, for example, all processing may becompleted and the final transcript would then be shown in texttranscription section 220.

In one embodiment, accuracy information from one or more of the multiplesearch passes can also be used on a word or utterance level.Illustration of this feature is provided by Text Segment 2, which isbroken down into words and/or utterances 1-12. Here, accuracyinformation (e.g., confidence scores) generated by a particular searchpass can be used to differentiate between the estimated accuracy ofdifferent words or utterances. For example, in one embodiment, words orutterances having confidence scores below a certain threshold can betargeted for differential display, such as that shown bywords/utterances 3, 6, 8, and 12. As would be appreciated, variouslevels of differentiation can be defined with associated levels ofshading, colors, patterns, etc. to communicate issues of relativeaccuracy in the transcribed text. In this manner, the accelerateddisplay of transcribed text would not hinder the user in hisappreciation of the data. Indeed, the highlighting of known or estimatedaccuracy issues, would enable the user to listen to specific portions ofthe speech content to discern words or utterances on his own. Forexample, the user interface can be designed to replay a specific portionof the speech content upon selection of a highlighted portion of thetranscribed text. Thus, it is a feature of the present invention thatthe user can work with transcribed text earlier than he otherwise wouldbe permitted to do so, and in a manner that is not hindered by the loweraccuracy of an initial or intermediate search pass.

Having described an exemplary user interface enabled by principles ofthe present invention, a brief description of a process of the inventionis now described with reference to the flowchart of FIG. 3. Asillustrated, the process begins at step 302 where an initial ASR pass isperformed on a speech segment. This initial ASR pass can represent anysearch pass that produces discernible transcribed output. At step 304,this transcribed output is displayed.

Next, at step 306, an additional ASR pass is performed on the speechsegment. As would be appreciated, this additional ASR pass can beinitiated after completion of the initial ASR pass, or can be performedcontemporaneously with the initial ASR pass. Regardless, it is expectedthat the additional ASR pass would produce discernible transcribedoutput after the initial ASR pass. At step 308, the transcribed outputfrom the additional ASR pass is used to update the initial display oftranscribed text.

It should be noted that the particular manner in which the transcribedtext from the additional ASR pass is used to update the display isimplementation dependent. In one embodiment, the displayed text itselfwould be modified. In other embodiments, an indicator on the displayreflective of the state of a multi-pass search strategy would beupdated. In still other embodiments, the relative highlighting or othercommunicated differentiator would be modified.

Embodiments within the scope of the present invention may also includecomputer-readable storage media for carrying or havingcomputer-executable instructions or data structures stored thereon. Suchcomputer-readable storage media can be any available media that can beaccessed by a general purpose or special purpose computer. By way ofexample, and not limitation, such computer-readable media can compriseRAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic diskstorage or other magnetic storage devices, or any other medium which canbe used to carry or store desired program code means in the form ofcomputer-executable instructions or data structures. When information istransferred or provided over a network or another communicationsconnection (either hardwired, wireless, or a combination thereof) to acomputer, the computer properly views the connection as acomputer-readable medium. Thus, any such connection is properly termed acomputer-readable medium. Combinations of the above should also beincluded within the scope of the computer-readable media.

Computer-executable instructions include, for example, instructions anddata which cause a general purpose computer, special purpose computer,or special purpose processing device to perform a certain function orgroup of functions. Computer executable instructions also includeprogram modules that are executed by computers in stand-alone or networkenvironments. Generally, program modules include routines, programs,objects, components, and data structures, etc. that perform particulartasks or implement particular abstract data types. Computer-executableinstructions, associated data structures, and program modules representexamples of the program code means for executing steps of the methodsdisclosed herein. The particular sequence of such executableinstructions or associated data structures represents examples ofcorresponding acts for implementing the functions described in suchsteps.

Those of skill in the art will appreciate that other embodiments of theinvention may be practiced in network computing environments with manytypes of computer system configurations, including personal computers,hand-held devices, multi-processor systems, microprocessor-based orprogrammable consumer electronics, network PCs, minicomputers, mainframecomputers, and the like. Embodiments may also be practiced indistributed computing environments where tasks are performed by localand remote processing devices that are linked (either by hardwiredlinks, wireless links, or by a combination thereof) through acommunications network. In a distributed computing environment, programmodules may be located in both local and remote memory storage devices.

Although the above description may contain specific details, they shouldnot be construed as limiting the claims in any way. Other configurationsof the described embodiments of the invention are part of the scope ofthis invention. For example, the invention may have applicability in avariety of environments where ASR may be used. Therefore, the inventionis not limited to ASR within any particular application. Accordingly,the appended claims and their legal equivalents only should define theinvention, rather than any specific examples given.

1. A method for reducing latency in automatic speech recognition, themethod comprising: transcribing speech data using a first automaticspeech recognition pass, which operates at a first transcription ratenear real time, to produce first transcription data; displaying thefirst transcription data on a display unit; determining, via a processorof a computing device, how many additional automatic speech recognitiontranscription passes are needed, wherein the additional automatic speechrecognition transcription passes are slower and more accurate than thefirst automatic speech recognition pass, to produce at least a secondtranscription data; and displaying an indication of how many additionalautomatic speech recognition transcription passes are forthcoming thatwill update the first transcription data displayed on the display unit.2. The method of claim 1, wherein the first automatic speech recognitionpass operates at real time.
 3. The method of claim 1, wherein the firstautomatic speech recognition pass operates at greater than real time. 4.The method of claim 1, wherein displaying the first transcription datafurther comprises displaying an indicator that signifies that moreaccurate transcription data is being generated.
 5. The method of claim1, wherein the first transcription data is displayed in at least one ofa different color and a different shade as compared to the indication.6. The method of claim 1, wherein portions of the first transcriptiondata having a relatively lower confidence score are distinctly displayedas compared to other portions of the first transcription data having arelatively higher confidence score.
 7. The method of claim 6, whereinthe portions of the first transcription data having the relatively lowerconfidence score are displayed in a darker shade as compared to theother portions of the first transcription data having the relativelyhigher confidence score.
 8. The method of claim 6, wherein the portionsof the first transcription data having the relatively lower confidencescore enable a user to listen to corresponding portions of the speechdata.
 9. The method of claim 1, wherein the additional automatic speechrecognition transcription passes of the speech data are normalizedautomatic speech recognition passes.